Presently, R-T-B (R is at least one rare earth element including Y, T is a transition metal including iron as a main component, and B is boron) rare earth magnets are actively used in various fields as high-performance magnets. Reuse of R-T-B rare earth magnets by way of recycling is important not only in view of the assurance and effective use of the resources, but also in view of the reduction in production cost of the R-T-B rare earth magnets.
In the case of the R-T-B sintered magnet, grinding sludge and fine powder generated in the production processes have a strongly oxidizing characteristic, so that they may disadvantageously cause spontaneous firing in the atmosphere. Accordingly, treatment in which the sludge and the fine powder are intentionally oxidized by a process such as incineration, so as to change them into stable oxides is performed. Chemical treatment such as acid dissolution is performed for such oxides, so that rare earth elements can be separated and extracted.
As for a final product of an R-T-B sintered magnet, it is studied that recycling to an R-T-B material alloy by means of a technique such as remelting is performed.
In the case where a bonded magnet is recycled, magnetic powder and a binder resin in the bonded magnet may be separated, thereby recovering the magnetic powder. However, the resin in the bonded magnet contains a lot of carbon component, so that it is difficult to avoid the carbon in the resin from adhering to the magnetic powder, or depositing and sticking thereto. As a result, the magnetic powder recovered from the bonded magnet includes a lot of impurities of carbon. Thus, it is necessary to perform a process of removing the carbon. The process of removing the carbon greatly increases the production cost, so that the recycling of the rare earth bonded magnet is not practically performed yet. In the case where an R-T-B sintered magnet with a resin film formed on the surface thereof is to be recycled, the same problem as that of the R-T-B bonded magnet exists.
Japanese Laid-Open Patent Publication No. 5-55018 discloses a technique in which a defective or unnecessary bonded magnet is pulverized into powder, and the powder is directly utilized again as magnet powder for a bonded magnet. However, the magnet powder included in the bonded magnet is magnetized, so that the magnetic powder still keeps the magnetism in a condition without any treatment. Thus, there exists a problem that it is difficult to supply such magnet powder to a cavity for compacting.
Japanese Laid-Open Patent Publication No. 7-111208 discloses a technique in which an unnecessary bonded magnet is heated up to 700 to 1000° C. in a vacuum or in an inert gas, thereby demagnetizing magnet powder. However, the thermal treatment at 700 to 1000° C. results in the following problems. Crystal grains in the magnetic powder become bulky, so that the coercive force is largely lowered. In addition, a resin in the bonded magnet is carbonized.
On the other hand, in a known method, a resin component in the bonded magnet is dissolved by using a solvent, thereby taking out magnet powder only. This method involves a disadvantage that the solvent to be used is expensive. In addition, the magnetic powder obtained by this method is in a magnetized condition, similarly to the magnetic powder obtained by the method of Japanese Laid-Open Patent Publication No. 5-55018, so that it is necessary to additionally perform a demagnetizing process.
The present invention has been conducted in view of the above-described prior art. A main object of the present invention is to recover a magnet alloy from an R-T-B bonded magnet or an R-T-B sintered magnet with a resin film on the surface thereof by a method without requiring a demagnetizing process or a decarburizing process, thereby enabling the R-T-B bonded magnet to be recycled.